The first step in diagnosing vestibular disease in the dog is differentiating peripheral and central vestibular disease. The neurologic exam performed by your veterinarian is the most important diagnostic tool. With a specialized scope, your veterinarian will assess the entirety of the ear canals. Advanced imaging, such as CT or MRI scans, is used to evaluate the boney inner ear, brain and spinal cord. Simple blood tests can determine your pet’s thyroid status.
The right ear canal in this CT scan is open and free of disease. The left has soft tissue filling the canal and middle ear as noted by the arrow.
If nystagmus is present, the direction will be an invaluable tool in differentiating peripheral from central vestibular disease. Peripheral nystagmus typically has a “fast phase away the lesion.” This means that the eyes will appear to “run away” from the side that the lesion is on. In this video, we can guess this dog’s lesion is on his right side.
Note that the fast phase is to his left. There are some exceptions to this rule, but they are rare. Central vestibular disease features vertical nystagmus (looking up and down, seen here) as well as positional nystagmus (only found when your dog is in certain positions.
The other hallmark of central vestibular disease is conscious proprioception (CP) deficits. Conscious proprioception is a tool your brain uses to know where your limbs and body are oriented. If you close your eyes, your brain knows where your hands and feet are by using this system (Law enforcement officers assess this system when looking for drunk drivers. They ask people to close their eyes and touch their finger to their nose testing the CP system). Central vestibular disease will almost always present with CP deficits. Sometimes signs are so complex that a veterinary neurologist must be consulted to identify the source of the lesion.
Further workup for central vestibular disease will often include advanced imaging such as a CT scan or MRI. These advanced techniques allow for non-invasive investigation of the inner ear, brain, and spinal cord. A CSF (cerebral spinal fluid) tap will help diagnose inflammatory or infectious CNS disease.